Sprains and strains occur when the body is put under stress. In these situations, muscles and joints are forced to perform movements for which they are not prepared or designed to perform. An injury can occur from a single stressful incident, or it may gradually come on after many repetitions of a motion. A strain occurs when the muscle tendon unit is stretched or torn. The most common reason for this is the overuse and stretching of the muscle. The damage may occur in 3 areas. The muscle itself may tear, the area where the muscle and tendon blend can tear or the tendon may rip away from the bone.
 

Joints are stabilized because thick bands of tissue called ligaments surround them. These ligaments only allow the joint to move in specific directions. Some joints move in multiple planes; therefore, they need more than one group of ligaments to hold each joint in the proper position. The ligaments are anchored to bone on each side of the joint. If a ligament is stretched or torn, the injury is called a sprain. Sprains and strains occur when the body is put under stress. In these situations, muscles and joints are forced to perform movements for which they are not prepared or designed to perform. An injury can occur from a single stressful incident, or it may gradually come on after many repetitions of a motion.